Molecular composites, which are blends of random-coil polymers reinforced by rigid-rod polymers, are known to possess properties superior to traditional fiber reinforced composites possessing the same weight fraction of reinforcing fiber. See, for example, Prevorsek, Polymer Liquid Crystals, Ed. by Ciferri, Krigbaum and Meyer, Academic Press, 1982, 361-376, who surveys the field of molecular reinforcement. Such composites lend themselves to the production of high strength workpieces suitable for high temperature environments. Among the techniques known for the preparation of such composites are extrusion and solution casting, but both have limitations which have prevented the preparation of homogeneous molecular composites with random or liquid crystalline orientation. Takayanagi and Kajiyama, U.K. Pat. GB No. 2,008,598B produced alloys of less than 20% of rigid rod-like homopolymers as well as blocks and grafts of rigid rod-like copolymers and greater than 80% of flexible coil-like polymers by blending solvent solutions, removing the solent, and hot pressing, and also by co-extrusion. Such techniques were also employed by Kanakalatha, Vijayan, Sridhar and Singh, Polymer, 1983, Vol. 24, May, pp. 621-625; and by Takayanagi, Ogata, Morikawa and Kai, J. Macromol. Sci-Phys., B17(4), pp. 591-615 (1980). Helminiak, Benner, Arnold and Husman, U.S. Pat. No. 4,207,407 and U.S. Pat. No. 4,377,546, disclose rod-like aromatic heterocyclic polymers used as reinforcements in coil-like heterocyclic polymer matrices to provide polymers at the molecular level that are analogous to chopped fiber composites. These are produced by blending dilute solutions of the respective polymers in methanesulfonic acid and removing the solvent from the polymer solution or by precipitating from solution by exposure to a moist atmosphere. Modifications, phase diagrams and properties of such polymer composites are given, inter alia, in Helminiak, Wellman, Hwang, Wiff, Rogers and Benner, Air Force Wright Aeronautical Laboratories Report, AFWAL-TR-80-4163, January 1980 to September 1980, dated February 1981, 79 pages; Helminiak, Hwang, Wiff, Benner and Price, Air Force Wright Aeronautical Laboratories Report, AFWAL-TR-82-4039, January 1980-August 1981, dated October 1982, 57 pages; Husman, Helminiak, Adams, Wiff and Benner, Molecular Composites (1980), 16, pp. 203-214; Hwang, Wiff, Benner and Helminiak, J. Macromol. Sci.-Phys. B22(2), 231-257 (1983); Hwang, Wiff, Helminiak and Adams, A.C.S. Organic Coatings and Applied Polymer Proceedings, 48, 929 (1983); Hwang, Wiff, Verschoore, Price, Helminiak and Adams, Polymer Engineering and Science, Mid-Octover 1983, Vol. 23, No. 14, pp. 784-788 (in which such solutions have also been extruded as fibers or films into coagulation baths); and Hwang, Wiff and Verschoore, Polymer Engineering and Science, Mid-October 1983, Vol. 23, No. 14, pp. 789-791. With respect to the properties of solvent cast composites, it was necessary to stretch and orient them to reinforce them, otherwise the rod-like polymer acted merely as a filler (Husman, Helminiak, Adams, Wiff and Benner); spun fibers needed to be drawn to maximize tensile strength (Hwang, Wiff, Benner and Helminiak); when rod-like poly(p-phenylenequinoxaline) (PPQ) was blended with coil-like nylon, it couldn't be oriented and therefore was not reinforced to the theoretical level (Hwang, Wiff, Helminiak and Adams); and wet drawn films and fibers were uniaxially oriented and strengthened in one direction only (Hwang, Wiff, Verschoore, Price, Helminiak and Adams).
It has now been discovered that in situ polymerization of a precursor of the coil-like polymer containing dissolved high strength (i.e., a tensile modulus above about 0.25.times.10.sup.6 psi) rigid rod-like liquid crystalline polymer in the form of liquid crystalline solutions will produce liquid crystalline molecular composites. Moreover, isotropic solutions will produce isotropic molecular composites. These orientations are desirable in many structural applications owing to the three-dimensional property enhancement.
The technique of in situ polymerization of monomeric solvent in the presence of low strength helical liquid crystalline polymers is known, e.g., Tsutsui and Tanaka, J. Polym. Sci. Polym. Lett. Ed., 15, pp. 475-478 (1977); Tsutsui, R. Tanaka and T. Tanaka, J. Polym. Sci. Polym. Lett. Ed., 17, pp. 511-520 (1979); and Tsutsui and Tanaka, J. Polym. Sci. Polym. Lett. Ed., 18, pp. 17-23 (1980). Further reports are given in Tsutsui and Tanaka, Chemistry Letters, pp. 1315-1318 (1976) who produced poly-L-glutamic acid rods with poly(ethylene oxide) chains; Tsutsui and Tanaka, Mol. Cryst. Liq. Cryst. Vol. 56 (Letters) pp. 57-61 (1979), and Tsutsui and Tanaka, Polymer, 1981, Vol. 22, pp. 117-123, who polymerized n-butyl acrylate in the presence of low strength poly(butyl-L-glutamic acid); and Tsutsui and Tanaka, Polymer Communications, 1980, Vol. 21, pp. 1351-2, who subjected poly(butylene-L-glutamate) dissolved in trimethylene glycol dimethacrylate to ultraviolet polymerization to provide films and molded articles for which no mechanical properties were given.
In view of the foregoing, it is new and unexpected now to utilize high strength rigid-rod liquid crystalline polymers in conjunction with the in situ polymerization technique and to find that molecular composites can be prepared for load bearing structural applications. The homogeneous isotropic and homogeneous liquid crystalline molecular composites so produced are new and form the subject matter of the present invention.